1. Field of the Invention
The present invention relates to a nonreciprocal circuit device, such as an isolator used in a high frequency band such as microwave band, and further to a communication apparatus using the same.
2. Description of the Related Art
Hitherto, a lumped-constant type circulator has been constructed by accommodating, within a case, a plurality of center conductors which intersect each other and which are disposed adjacent to a ferrite plate, and a magnet which applies a DC magnetic field to the ferrite plate. Also, an isolator is formed by terminating one predetermined port of the three ports thereof by a resistor.
FIG. 4 is an exploded perspective view illustrating a conventional isolator. Herein, reference numeral 2 designates a box-shaped upper yoke formed of a magnetic metal, and 3 designates a rectangular plate-shaped permanent magnet which is to be disposed on the inner surface of the upper yoke 2. Reference numeral 5 designates a magnetic assembly. The magnetic assembly 5 has a construction wherein a ferrite 54 is disposed on the coupling portion of center conductors, the coupling portion having the same shape as that of the bottom surface of the disk-shaped ferrite 54, wherein three center conductors extending from the coupling portion are folded so as to wrap the ferrite 54 in a state of intersecting one another at an angle of 120xc2x0, and wherein the port portions P1, P2, and P3 on the tip sides of the center conductors are projected outward, respectively. Reference numeral 4 denotes a spacer for keeping the gap between the magnetic assembly 5 and the permanent magnet 3 at a predetermined spacing, and 7 denotes a resin case. Matching capacitors C1, C2, and C3 are connected between the respective port portions P1, P2, and P3, and a ground electrode in the resin case 7. A terminating resistor R is connected between the electrode conducting to the port portion P3 and the ground electrode. Reference numeral 8 denotes a lower yoke formed of a magnetic metal, which forms a closed magnetic circuit by being combined with the upper yoke 2.
The conventional isolator shown in FIG. 4 uses a disk-shaped ferrite, and has the structure as shown in FIGS. 5A and 5B in order to dispose the three center conductors adjacent to the ferrite so as to intersect one another with a cross angle of 120xc2x0. FIG. 5A is a view showing the center conductors before being folded, that is, a development view thereof. FIG. 5B shows the center conductors which are being folded. Here, the portion indicated by reference numeral 50 is the center conductor coupling portion. From this center conductor coupling portion, the three center conductors 51, 52, and 53 are led out in three directions, and the tip portions thereof define the port portions P1, P2, and P3, respectively. The magnetic assembly 5 shown in FIG. 4 is formed by placing the ferrite 54 on the top surface of the center conductor coupling portion 50, in the configuration shown in FIG. 5A, and by then folding the three center conductors 51, 52 and 53 so as to wrap the ferrite 54, as shown in FIG. 5B.
As a method for bending the center conductor, a method can be adopted wherein the ferrite is abutted against the center conductor coupling portion, and while utilizing this push force, each of the center conductors extending from the center conductor coupling portion in the radial directions is once raised at an angle of about 30 to 70xc2x0. This is an effective method when the center conductors are bent by means of an automatic machine.
Meanwhile, the port portions provided at the tips of the center conductors are connected to the input/output terminals or the capacitors. In order to enhance the quality of the bonding portions with the input/output terminals and the capacitors, it is necessary to ensure sufficiently large bonding areas. For this purpose, it is desirable to form the port portion at the tip part of each of the center conductors into a size as large as possible.
In the resin case having a rectangular shape in a plan view as a whole, in order to make the volume of the magnetic body coupled with the center conductors as large as possible, as well as to facilitate the molding of the magnetic body, it is effective to use a magnetic body having a rectangular shape in a plan view (i.e., a magnetic body of a rectangular parallelepiped). FIG. 6 shows the shapes of the center conductors when a magnetic body having a rectangular shape in a plan view is used. In the configuration shown in FIG. 6A, the ferrite 54 is placed on the top surface of the center conductor coupling portion 50, and firstly the center conductor 51 is folded. Then, when attempting to fold the center conductor 52, the port portion P1 at the tip part of the first center conductor 51 can interfere with the second center conductor 52, as indicated by a mark ◯ in FIG. 6B, thereby not allowing the second center conductor 52 to be bent. One solution to this problem is to form the port portion at the tip part of one center conductor into a smaller size so as not to interfere with the other center conductor. However, this raises a problem that the bonding areas between the port portions and the capacitors or the input/output terminals cannot be sufficiently ensured, resulting in a reduced reliability of the bonding portions.
Accordingly, it is an object of the present invention to solve the above-described problem, and to provide a nonreciprocal circuit device which prevents the center conductors thereof from interfering with each other when folded toward a magnetic body even when the magnetic body has a rectangular shape in a plan view, and which thereby increases the reliability of the bonding portions between the port portions at the tip parts of the center conductors and the capacitors or the input/output terminals, and further to provide a communication device using this nonreciprocal circuit device.
In accordance with a first aspect of the present invention, there is provided a nonreciprocal circuit device comprising a plurality of center conductor, a magnetic body placed on the coupling portion of the center conductors, and a magnetic assembly in which the center conductors extending from the coupling portion outward are folded so as to wrap the magnetic body. In this nonreciprocal circuit device, the magnetic body is formed as a rectangular shape, and the port portions of the center conductors which are to be connected to the capacitors or the input/output terminals are formed asymmetrically with each other so as not to mutually interfere when the center conductors are folded toward the magnetic body.
By these structures, the center conductors can be prevented from an interference when they are folded, without the need to reduce the size of the port portion at the tip part of each of the center conductors.
In the first aspect of the present invention, preferably, the port portion of one of the two center conductors which extend from the coupling portion outward substantially line-symmetrically, is formed smaller than the port portion of the other center conductor. In virtue of this structure, when folding the two center conductors so as to wrap the magnetic body, by folding the center conductor having a smaller port portion earlier and folding the other center conductor later, the port portion of the center conductor which has been already bent can be prevented from interfering with the other center portion, and the port portion of the center conductor to be folded later can be provided with a sufficiently large size.
Also, in the first aspect of the present invention, it is preferable that at least one of a notch or a hole be formed in the port portions. This structure increases the area of the solder fillets when the port portions are soldered to the capacitors or the input/output terminals, thereby enhancing the reliability of the bonding portions.
A second aspect of the present invention provides a communication apparatus using the above-described nonreciprocal circuit device.
The above and other objects, features, and advantages of the present invention will be clear from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings.